<template>
  <div class="box">
    <span>{{num}}</span>
    <button @click="sum">+</button>
  </div>
</template>

<script>
export default {
    data(){
        return {
            num:0,
        }
    },
    methods:{
        sum(){
            this.num++
        }
    }
}
</script>

<style>
.box{
    display: flex;
    height: 100vh;
    justify-content: center;
    align-items: center;
}
</style>